In the manufacture of automotive vehicles such as passenger cars and trucks, there are many safety standards that must be met by the vehicle to reduce the likelihood and/or severity of injury to occupants during a crash event.
In order to meet these safety standards, portions of the vehicle, for example interior structures such as the instrument panel assembly are required to absorb at least some of the energy of an impact of an occupant during a crash event. To achieve this, the instrument panel assembly may implement one or more energy absorbing structures known as a bolster. For example, a knee bolster assembly may be implemented to absorb energy in the event of an impact from the knees of a vehicle occupant during a crash event. In general, energy absorption is achieved through deformation of the bolster structure.
Passive bolster assemblies may additionally use specialized structures to assist with energy dissipation. For example, some passive bolster assemblies incorporate energy absorbing brackets. In some forms, these brackets dissipate the energy by way of controlled deformation of the bracket structure during the crash event.
In many current designs, the bolster forms a portion of the surface of the instrument panel, and therefore must meet certain appearance characteristics. Many bolster systems are made from injection-molded parts, which have good appearance characteristics on the surface which is visible within the vehicle. However, in order to achieve these appearance characteristics, injection molded parts must be formed within certain design parameters. For example, to avoid warping and shrinkage issues, injection molded parts are often provided with wall structures of 3 mm or less, thus limiting the overall strength of the bolster system. To compensate, the injection-molded bolster component is mated to a metal back-plate for overall strengthening. These components are ultimately connected to the vehicle structure using separately formed brackets, designed to provide the energy absorbing characteristics of the overall bolster system.
Bolster systems constructed in this way, that is having an injection molded component, a metal back-plate, and bracket structures are complicated and expensive structures to manufacture. In addition, conventional passive bolster systems have been known to produce load-deflection profiles that are not optimal for injury mitigation. For example, conventional passive bolster systems generally exhibit a non-uniform deformation resistance, as well as excessively long displacement to dissipate a given quantity of energy. As a result, typical load-deflection profiles for conventional bolster systems show one or more peak loads that are high with respect to recommended limits. Accordingly, there exists a need for a more simplified overall construction capable of achieving a load deflection profile that effectively dissipates energy in a controlled manner, with shorter overall displacement, and within recommended injury threshold limits.